(57) An array of ultrasonic transducer elements receives signals to form beams simultaneously from a plurality of beam directions. The echo signals received by each transducer element are sampled in response to two or more interleaved sampling signal sequences, each of which is timed to begin at the initial time of arrival of echo signals from a unique spatial line. Each sampling signal sequence thereby produces signal samples associated with a given line. The stream of interleaved signal samples from each transducer element are separated in correspondence with each sampling signal sequence, and signal samples from corresponding separated sequences from the transducer elements are summed to form coherent signals corresponding to spatially separate ultrasonic beams.